10.
When to use YUI• You already know what JavaScript is• To build full-fledged websites that have numerous components with interdependent dependencies• You need lot of build-in widgets• Need to use design patterns• Need to have a maintainable code

11.
When to use jQuery• If you are new to JavaScript• Want something that is light• Have a simple website with lesser number of components• Need a quick solution and want something that is easier to learn

12.
When to use backbone.js• Decouple data from the UI• Use a full fledged MVC in the client side as well• Want to have multiple views/clients (mobile, desktop, tablets etc)• You have a clear understanding of JavaScript and also the MVC concepts

22.
When to use node.js• Writing highly concurrent server applications• Sharing application logic between server and client• Peer-to-peer web applications using websockets• And node.js is available in Azure